The present invention generally relates to the field of lubricant applicators and more specifically to a lubricant applicator which utilizes a venturi nozzle to draw powder from a fluidized hopper.
Since the beginning of powder metallurgy, lubricants have been added to metal powders to facilitate the removal of green powdered metal parts from the pressing dies. These lubricants must be subsequently removed from the parts during the sintering process. Numerous problems can result from using internal lubricants in powder metallurgy. These include coating of the sintering furnace interiors and incomplete lubricant removal. The former leads to a less effective sintering process and increased maintenance, while the latter leads to blistering and porosity. Other internal lubricant related problems include reduced green strength, reduced tensile strength of sintered parts, lower part density, reduced particle-to-particle compaction during pressing, and reduced particle-to-particle cementation during sintering.
Replacing internal lubricants with external lubricants will reduce and/or eliminate a number of the problems associated with internal lubricants in powder metallurgy. External lubricants applied to the surface of the pressing dies and transferred to the green powdered metal parts can be more readily removed from the parts than internal lubricants. Lower viscosity liquid lubricants capable of releasing the parts from the dies may penetrate the surface of the parts more than higher viscosity liquid lubricants making their removal from the parts more difficult than high viscosity liquids. A solid external lubricant applied to the die surface is not likely to penetrate the green powdered metal parts' surface at all and be more readily removed from the parts.
External solid lubricants capable of releasing the green powdered metal parts from pressing dies exist, as do applicators for applying the powdered lubricants. One such applicator proposed by the assignee of the present application is the applicator disclosed in U.S. Pat. No. 5,400,921. The '921 patent discloses a particulate material delivery apparatus comprising a measuring device for separating a predetermined quantity of particulate material from a particulate material supply. A first valve is provided responsive to a single input signal to regulate a control fluid and a delivery fluid. An actuator shifts a measuring device between measuring and delivery positions in response to a pressure signal from the first valve. A control apparatus dispenses a pressurized delivery fluid for a variable, predetermined interval of time in response to a pressure signal from the first valve. A method for delivery of measured charges of particulate material is also provided. The method of the '921 patent comprises the steps of discharging one charge of the material to a first location, measuring a second charge of the material and delivering the first charge to a remote location while measuring the second charge. However, a need remains for an improved applicator.